Cisco Systems 3750E manual Mapping Tables, 36-12

Chapter 36 Configuring QoS

Understanding QoS

Mapping Tables

During QoS processing, the switch represents the priority of all traffic (including non-IP traffic) with an QoS label based on the DSCP or CoS value from the classification stage:

•During classification, QoS uses configurable mapping tables to derive a corresponding DSCP or CoS value from a received CoS, DSCP, or IP precedence value. These maps include the CoS-to-DSCP map and the IP-precedence-to-DSCP map. You configure these maps by using the mls qos map cos-dscpand the mls qos map ip-prec-dscpglobal configuration commands.

On an ingress port configured in the DSCP-trusted state, if the DSCP values are different between the QoS domains, you can apply the configurable DSCP-to-DSCP-mutation map to the port that is on the boundary between the two QoS domains. You configure this map by using the mls qos map dscp-mutationglobal configuration command.

•During policing, QoS can assign another DSCP value to an IP or a non-IP packet (if the packet is out of profile and the policer specifies a marked-down value). This configurable map is called the policed-DSCP map. You configure this map by using the mls qos map policed-dscpglobal configuration command.

•Before the traffic reaches the scheduling stage, QoS stores the packet in an ingress and an egress queue according to the QoS label. The QoS label is based on the DSCP or the CoS value in the packet and selects the queue through the DSCP input and output queue threshold maps or through the CoS input and output queue threshold maps. You configure these maps by using the mls qos srr-queue{input output} dscp-mapand the mls qos srr-queue{input output} cos-mapglobal configuration commands.

The CoS-to-DSCP, DSCP-to-CoS, and the IP-precedence-to-DSCP maps have default values that might or might not be appropriate for your network.

The default DSCP-to-DSCP-mutation map and the default policed-DSCP map are null maps; they map an incoming DSCP value to the same DSCP value. The DSCP-to-DSCP-mutation map is the only map you apply to a specific port. All other maps apply to the entire switch.

For configuration information, see the “Configuring DSCP Maps” section on page 36-63.

For information about the DSCP and CoS input queue threshold maps, see the “Queueing and Scheduling on Ingress Queues” section on page 36-15. For information about the DSCP and CoS output queue threshold maps, see the “Queueing and Scheduling on Egress Queues” section on page 36-18.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
36-12	OL-9775-02